An MRI apparatus is an apparatus for imaging an arbitrary cross-section across a subject using a nuclear magnetic resonance phenomenon. Specifically, the MRI apparatus is an apparatus for acquiring a sectional image by performing an image processing after irradiating atomic nuclei (usually hydrogen nuclei) in a subject placed in a spatially-uniform magnetic field (static magnetic field) with a radio frequency magnetic field, rotating macroscopic magnetization by atomic nuclei (magnetic resonance) with the direction of the static magnetic field as an axis, and detecting (receiving) a rotating magnetic field (circularly-polarized wave) generated in the process of returning to the original state while being rotated, as a nuclear magnetic resonance signal. In general, the direction of rotation of atomic nuclei is determined by the relationship between the static magnetic field direction and the nuclei.
Irradiation of a radio frequency magnetic field on a subject and detection of a nuclear magnetic resonance signal generated from the subject are performed by an RF coil having a loop part (coil loop) that performs an irradiation and detection. As the coil loop becomes smaller, a sensitivity region becomes narrower but the sensitivity becomes higher. In the meantime, as the coil loop becomes larger, the sensitivity region becomes wider but the sensitivity becomes lower. In this way, the RF coil has a trade-off relationship between the high sensitivity and the wide sensitivity region. Since this nuclear magnetic resonance signal is a very weak signal, high sensitivity is required for the RF coil.
There is a multi-channel array coil in which a plurality of RF coils is arranged in an array to achieve both high sensitivity and a wide range of sensitivity (see, e.g., Non-Patent Literature 1). Hereinafter, each RF coil in the multi-channel array coil is called a sub-coil.
In recent years, high-speed imaging using a difference in spatial sensitivity between sub-coils of the multi-channel array coil has become widespread (see, e.g., Non-Patent Literature 2). The high-speed imaging may be accelerated with the increased number of channels. Therefore, in recent years, the multi-channelization of multi-channel array coils has been further advanced to super multi-channel array coils of 32 channels and 128 channels which are now being distributed.